It's a well known practice for online retailers to track your browsing habits on their site so that they can highlight products based on your preferences. But retailers are increasingly tracking you when you're inside their physical stores too.

The New York Times reports on Euclid Analytics, a company that sells WiFi antennas to retailers wanting to know more about customer shopping habits. By picking up signals that smartphones give off, even when you're not using the phone, stores can get an idea for how many people enter the store, how long they stay, and where they browse.

The big initial use is the so-called bounce rate, or the percentage of people who come into the store who leave without making a purchase. But the technology also helps stores make sure that there is enough sales help or that enough registers are open. By seeing how people move in a store, retailers can also better determine where to place low-profit and high-profit items.

According to the Times, the three-year-old company already has 100 customers -- Nordstroms and Home Depot among them -- and has tracked 50 million devices in 4,000 locations.

Privacy is always a concern when it comes to this kind of tracking. The company assures that the collected data is anonymous. But really, I don't think privacy is a big deal in this case. Let's face it, if you use a smartphone or computer you're leaving digital traces everywhere. There's something uncomfortable about it, but I think we're growing more comfortable with this reality. If you're not, you should stop browsing the Web and using your phone. Plus, if this technology can make for a better customer experience, it's a benefit to everyone.